Electroacoustic transducer



May 9, 1950 R. E. wlRscHlNG ELEC'IRGACOUSTICv TRANSDUCER Filed June 18, 1947 n @mmm FIGu Z This invention relates Patented May 9, 1950 ELECTRGACOUSTIC TRANSDUCER Robert E. Wrsching, Chatham, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 18, 1947, Serial No. 755,397

12 Claims. 1 i to electroacoustlc transducers and more particularly to ring armature type acoustic devices such as disclosed in the application Serial No. 704,483, filed October 19,

1946, of Edward E. Mott.

' In ring armature type transducers of the general construction disclosed in the above-identified application, the magnetic system includes two magnetic circuits each of which comprises a permanent magnet and also an annular armature common to the two circuits. The armature is supported adjacent its outer portion and has its inner marginal portion extending into an air gap between juxtaposed magnetic parts of the two circuits. The magnets in the two circuits are relatively poled so that the components of ux through the armature due thereto are in opposition.

Realization of optimum performance by such 'construction entails manufacture of the parts constituting the magnetic system to close tolerances. In known constructions, the magnetic system comprises a relatively large number of parts so that the structure is somewhat complex and attainment of the desired relation of the parts involves manufacturing control of a correspondingly large number of parts.

One object of this invention is to simplify the structure and facilitate the manufacture of ring armature type transducers.

More specifically, objects of this invention are to reduce the requisite number of elements or :parts in magnetic systems for transducers of the general construction above-described, to expedite the realization of the correlation of the elements or parts to assure optimum performance,

'and to facilitate the manufacture of such trans- Vprovide a reference surface for determining the .normal position of the armature in the air-gap ofthe assembly. Advantageously, the support member is of non-magnetic non-metallic material So that eddycurrent losses in the magnetic system are minimized.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanyingr drawing in which:

Fig. 1 is a side'view section of an electroacoustic transducer illustrative of one embodi- 'ment of this invention;

Fig. 2 is a detail diagrammatic view illustrating the direct current and signal ux paths in the transducer shown in Fig. 1, and

Fig. 3 is a fragmentary sectional view illustrating another embodiment of this invention.

Referring now to the drawing, the device therein illustrated is operable as either a receiver or transmitter and comprises a pole-piece having an annular base Io and a cylindrical pole tip portion II, the 'pole-piece being of a material, such as the nickel-iron alloy known commercially as Permalloy, having a high permeability. Associated with the pole-piece i3, II is an annular permanent magnet having a cylindrical portion I2 coaxial with the pole tip portion I I and seated upon the base I0 and an integral annular flange I3 the inner marginal part of which is opposite and coaxial with the tip of the pole-piece portion I i. The magnet is of a high coercive force material such as the aluminum-nickel-cobaltiron alloy known commercially as Alnco or the molybdenum-cobalt-iron alloy known commercially as Remalloy.

A cylindrical non-magnetic support I4 is seated upon and nrmly afxed to the base I0, is tted within the magnet part I2 and has its other end coplanar with the tip face of the pole-piece p0rtion II. Advantageously, the support is of a non-metallic material which is easily machinable so that the free end face thereof may be readily operated upon, e. g. ground, to make it accurately copla-nar with the pole tip face. A suitable and illustrative material is a phenolic condensation product. Seated upon and aixed to the support I4 is an annular magnetic spacer I5, for example of Permalloy, which is fitted within the cylindrical lpart I 2 of the magnet and forms a seat for the armature I B. The armature, which also may be of Permalloy, is annular, has its periphery immediately adjacent the magnet and has'its inner marginal portion coaxial with and in juxtaposition to the face of the pole tip portion II.

The armature mounts a dished, lightweight non-magnetic diaphragm I7, for example of thin metal such as Duralumin, a plastic such as polystyrene, or a fabric impregnated with a phenolic condensation product.

overlying the armature and aixed to the flange I3 o'f the magnet isa non-magnetic annulus la 'which serves to prevent contact of the armature with the -magnet flange I3 andvsticking of the armature thereto.

A centrally dished and apertured disc or grid I9 is seated upon the flange I3 and serves to protect the diaphragm I'I. At the other end ofthe s tructure is an insulating pla-te 20 mounting terminals 2| to which the ends of a cylindrical sigyportion I I; v'assigned ythickness and, thusQxes the .normal gap nal coil 22 mounted between the pole-piece il and support M, are connected.

The severalparts of the structure, specilcaliy the magnet', pole-piece, grid and terminal are firmly held together in pile-up relation by a ID. In the latter case, the support provides eddy current shielding of the magnet part I2.

clamping band 24 having its ends bearing against between the armature andv the poleztip'face.. It

will beappreciated, thereioregthat the structure isfcapable of ready :assembly and that .manufacture thereof in quantity and atrelatively low cost is expedited.

.The Amagnetic system of.; the transducer comprises two circuitsfior branchesfhaving the arma- HLLIIV and major partof portion I 2 ofthe permanent magnet.

It will k.be noted that there are two oppositely directed components 'of .direct current flux threadingy the armature |16.` f Intransducers ofthe type disclosed, it is advantageous, as pointed out in "Patent 2,249;160, granted Julyl, 1941, to Edward Mott, that these twofux components be unequalv whereby an unbalance in theV two circuits or branchesoi the system obtains.l In transducers .of the' construction hereindisclosed suchunbalance, as Vwellas-correlation of the magnetomotive VYforces to lassure ymaximum Veiliciency and operating stability are iacilely; achieved.

Specically, inthe manufacture of thev transducen the magneti'Z., I3 is magnetizedto produce lpoles .ci opposite polarity atits extremities-as lindicated at N ands in FigiA 2. Then acurrent is: supplied-to the coil ZZ-in the. direction to demagnetizeV the magnet part vI2A thereof, in steps` to the point corresponding .to maximum eiiiciency.

Finally, the portion` I3 ofthe magnet isf-demag- Vnetized insteps, asby anielectromagnetapplied across the ends thereof, tothe .point correspond.-

ing to a desirable operating stability for the. transn ducer. In the `completed device, then, the direct current. Vflux component.. in. thefarmature. which iowsin the branch or circuit including the polepiece and magnet part I2V is greater than the component which ows inthe branch or circuit .lncludingthemagnet part I3.

. `In the embodiment .of thel invention illustrated ...iin Eig. 3,.,thearmature support/comprises a cylindrical part H3A ntted within they magnet portion I-2 and an annular iiange-g-IAB seated'upon and aixed to the base iiange IU .of the pole-piece. .The support maybe, of insulating material and have its portion IB,` cemented to thepole-piece "flange It. .lilternativeln4 the support may be `of Jagfhigh resistivity metal havingslight permeability and have its portion IIB welded'to the ange The free endof the supportk portionzIlIA and the tip of pole-piece portion I l are ground plane and are in parallel planes, and the armature IB is seated directly upon the support I4. In the lfabrication of the device, the free end of magnet part l2 is ground to establish a prescribed distance between .the plane of this end and the magnet-part I3. Then the free end of support portion IGA is ground to x the distance thereof frornfthewireeend of magnet part I2 at a prescribed value. Finally, the tip of pole-piece portionY I l is ground so that it is in a plane a preassigned distance fromthe plane of the free end ci support portion 14A. Consequently, when .the

'elements are assembled', preassigned normalspacings between 'the armature and the .tip of polepiece y,portion l1 andthe magnetpart |31 obtain.

As in the device illustrated in Figs.. lfand, in the construction shown in Fig. 3, the magnet is magnetizedto produce poles atfitslextremes-and then is -demagnetizedsectionally to establish the desired unbalance between thel two-circuits-.cr branches of the magnetic system` and. realize maximum eiiiciency` and a` desirable operating stability. Y

Although specific embodiments ofthe invention have been shown and described, it vwillxbefunderstood that they are but.illustrativa. and Ythat lvarious modifications may be made therein- .without-'departing from the scopeand spirit lof this invention as dened in the appended claims;

What is claimedis:

l. .en electroaccustic.transducer comprisinga pcie-piece navi-nga. base'and a cylindrical portion extending from said base, av magnet. having. .-.a cylindrical portion Vextending from said `basearld coaxial with-said cylindrical portion of saidpolepiece, saidmagnet having-also a ange" portion in juxtaposition to said cylindrical portionotVv said pole-piece and dening an air -gap therewith, an annular armaturehaving one .margin adjacent a part ci said .magnet intermediate the` poles thereof and having a portionextending. intosaid-air and meanssupporting saidv armaturefor vibratorymotion of said portionthereof. y

2. An electroacoustictransducer comprising a magnet having a cylindrical portionand .an annular fiange Vextending inwardly -from .one end of said cylindrical portiorna pole-piece.v extending inwardly from theother endr of sa-idicylin.- drical portion and havingan annular poletipin juxtaposition to said ange and -deflninganair gap therewith, an annular armaturehaving.- its periphery adjacent said cylindrical portion of said magnet vand having a-portion in said air gap, and means supporting said armature adjacent said periphery thereof. Y Y

3. `An electroacoustic transducer. comprising a pole-piece .having a. base and.. a pole. tip v.portion extending. from said. base, a. magnet. hai/inge portion one end of whichis adjacent saidbase and having also. a flange extending from` the other end of' said' portion. saidange Yhavinglits free end in juxtaposition to said pole ,tip .portion and deiining an air gap therewith, said magnet `being .magnetized `toQproduce polesofv opposite said air gap.

polarityl at said one and free ends and such that parts extending fromV said oneand other'ends are of unequal strength, and an armature'having one margin immediately` adjacent ,anV intermediate portionofsaid magnet` and extending into 4. An'r electroacoustic" transd'ucerVVV comprising a magnetY having a cylindrical portion and-anannular flange extending from one end of said cylindrical portion, a pole-piece having a base extending from the other end of said cylindrical portion and having also a cylindrical pole tip in juxtaposition to and coaxial with the free end of said flange and defining an air gap therewith, said magnet being magnetized locally to produce poles of opposite polarity at said one end thereof and said end of said flange and such that said cylindrical portion and flange are 'of unequal strength, an annular armature having one margin immediately adjacent the junction of said cylindrical portion and flange and its other margin in said air gap, and means supporting said armature adjacent said one margin thereof.

5. An electroacoustic transducer comprising a magnet having a cylindrical portion and an annular flange extending inwardly from said cylindrical portion, a pole-piece comprising a base extending inwardly from one end of said cylindrical portion `and a cylindrical pole tip portion coaxial with said flange and terminating in a tip in juxtaposition to the inner margin of said flange and defining an air gap therewith, said magnet being magnetized locally to produce poles of unlike polarity at said one end and margin and such that said cylindrical portion is more highly magnetized than said flange, an annular armature having its outer edge adjacent the junction of said cylindrical portion and flange and its inner edge portion in said air gap, and means supporting said armature adjacent said outer edge thereof.

6. An electroacoustic transducer comprising a pole-piece having a cylindrical portion terminating in a pole tip and having also a iiange extending from said cylindrical portion, a magnet having a cylindrical part seated upon said flange and spaced from said cylindrical pole-piece portion and having also a flange overlying said pole tip and defining an air gap therewith, a cylindrical support between said cylindrical magnet part and said cylindrical pole-piece portion, and an annular armature seated adjacent one margin upon said support and extending into said air gap.

7. An electroacoustic transducer in accordance with claim 6 wherein said support is alhxed to said pole-piece in coaxial relation with said cylindrical pole-piece portion and is fitted to said cylindrical magnet part, whereby said cylindrical portion is positioned coaxially with respect to said part.

8. An electroacoustic transducer in accordance with claim 6 wherein said support is affixed at one end to said flange of said pole-piece and has its other end coplanar with said pole tip, said transducer comprising also a spacer member upon said other end of said support, and said armature being seated upon said spacer member.

9. An electroacoustic transducer in accordance with claim 6 wherein said support is of insulating material.

10. An electroacoustic transducer comprising a pole-piece having a cylindrical portion terminating at one end in an annular pole tip and having also an annular flange extending outwardly from the other end of said portion, a permanent magnet having a cylindrical part coaxial with said cylindrical portion and seated at one end upon said flange, said magnet having .also an annular flange extending inwardly from the other end yof said cylindrical part and with its inner margin in juxtaposition to and defining an air gap with said pole tip, a cylindrical non-magnetic support encompassing said cylindrical pole-piece portion and adjacent said cylindrical magnet part, said support being seated at one end upon said poleplece part and having its other end coplanar with said pole tip, a spacer member upon said other end of said support, and an annular armature having its outer marginal part seated upon said spacer member and its inner marginal part in said air gap, said magnet being magnetized to produce poles of opposite polarity at said one end thereof and said inner margin of said flange and such that said cylindrical part is more highly magnetized than said iiange.

11. An electroacoustic transducer :comprising a magnet having a cylindrical portion and an annular flange extending from one end of said cylindrical portion, an annular armature having one margin adjacent said cylindrical portion and its other margin opposite the free end of said flange, said flange and armature together with the gap therebetween and a portion of said cylindrical portion defining a first magnetic circuit, a pole-piece extending from the other end of said cylindrical portion and having a pole tip in juxtaposition tc said other margin of said armature, said pole-piece and armature together with the gap therebetween and the remainder of said cylindrical magnet portion defining a second magnetic circuit, and a signal coil linked to said second circuit, said magnet being magnetized to produce poles of unlike polarity at said other end of said cylindrical portion and said free end of said flange and such that the direct current inagnetomotive force in said second circuit is greater than that in said first circuit.

12. An electroacoustic transducer comprising a permanent magnet having a cylindrical portion and an annular iiange extending inwardly from one end of said cylindrical portion, a pole-piece extending inwardly from the other end of said cylindrical portion and having an annular pole tip in juxtaposition to and coaxial with the inner margin of said flange, an annular armature having its periphery adjacent said one end of said cylindrical portion and having its inner marginal part in the gap between said pole tip and said inner margin of said flange, and a signal coil linked to said pole-piece, said magnet being magnetized to produce poles of unlike polarity at said other end of said cylindrical portion and at said inner margin of said flange and such that the direct current flux in the magnetic circuit including said armature and said pole-piece exceeds that in the magnetic circuit including said armature and said flange.

ROBERT E. WIRSCHING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,228,639 Bayer July 5, 1917 1,579,605 Gavin Apr. 6, 1926 1,895,071 Fanger Jan. 24, 1933 1,951,531 Ringel Mar. 20, 1934 2,170,571 Mott Aug. 22, 1939 2,249,160 Mott July 15, 1941 2,395,166 Collins Feb. 19, 1946 

